The present invention relates to a drive control system of a brushless motor and a technique effective in use for the speed control of the motor. As an example, it relates to a technique effective in application to a semiconductor integrated circuit for driving and controlling a spindle motor that drives to rotate a disk storage medium such as a magnetic disk of a hard disk drive, and a motor drive control device using the integrated circuit.
The hard disk drive generally uses a DC brushless multi-phase motor as the so-called spindle motor. The hard disk drive rotates a magnetic disk at a high speed by means of the spindle motor, brings a read/write magnetic head close to the surface of the rotating magnetic disk, and writes or reads information while moving it in the radial direction. The invention concerning the drive control device of the spindle motor in a hard disk drive is disclosed, for example, in the Japanese Unexamined Patent Publication No. 2003-111485 (here under, referred to as Patent Document 1).